Introduction to the Plus range

Spanish Amstrad 6128 Plus

Custom Airbrushed 6128 Plus

In 1990 Amstrad introduced the "Plus" range which tweaked the hardware in many ways and added a cartridge slot to all models. The Plus included the 464 Plus, 6128 Plus and the GX4000 video game console (which is a cut down Plus without the keyboard nor support for non-cartridge media). All of the range included a cartridge slot and additional hardware improvements.

Most improvements were to the video display which saw an increase in palette to 4096 colours and gained the capability of hardware sprites. Splitting the display into two separate windows and pixel scrolling both became full supported hardware features although both were possible on the non-"Plus" hardware using clever programming of the existing Motorola 6845. An automatic DMA transfer system for feeding the sound chip was also added but the sound chip itself remained unchanged. Additionally, the BASIC command set for disc access was improved.

These models did not do very well in the marketplace, failing to attract any substantial third party support. The 8-bit technology behind the Plus was starting to look a little out of date by 1990 and users resented the substantial price hike for cartridge games compared to their tape and disc counterparts. However, the Plus machines did sell well in France where Amstrad still had a large following due to the success of the classic CPC range there.

The range was officially titled as 'Amstrad 464 Plus', 'Amstrad 6128 Plus' and 'GX4000' and the 'CPC' (standing for Colour Personal Computer) abbreviation used in the older generation was dropped. However, many Amstrad users refer to the Plus range as 'CPC Plus' or 'CPC+' due to the inherent similarities of the two ranges.

The GX4000 Games Console

Amstrad GX4000

Amstrad GX4000

The GX4000 is a game console based on a 6128 Plus without a floppy controller or keyboard (although it is actually possible to modify one, add a floppy controller and a keyboard and use it as a Plus). It was delivered with two game paddles (as the ones delivered with the Plus models) and Burnin' Rubber on cartridge (without BASIC).

The GX4000 was Amstrad's attempt to gain some share in the home game console market, then dominated by the likes of Nintendo and Sega. Like others before it, and like others after it, it failed abysmally in its goal. Despite the fact that the hardware was decent (after all the CPC+ series were some of the very best 8-bit computers ever designed), it was a case of 'too little, too late'. Lack of CPC+ specific software, lack of marketing effort and bad timing meant that Amstrad's adventure in the home market was about to end.

GX4000 differences compared to 464 or 6128 Plus

The master clock is 39.9Mhz (approx) instead of 40Mhz for the 464/6128 Plus. The Arnold V specification indicates this is to give a better picture. This means the GX4000 is 0.25% slower than a 464 or 6128 Plus but should have a better picture.

The pause button on the GX4000 is mapped to the P button on the CPC keyboard. Other than this the 2 digital joysticks are connected, all other keys are not connected.

There is a difference in the wiring schematics on the ADC inputs where the ASIC senses the computer configuration.

The following are not connected on GX4000 so the associated inputs are not defined (possibly high):

When a system cartridge is inserted (this has been verified with a yellow and a green labelled system cartridge), the copyright message and a Ready prompt is displayed. If the fire buttons or directions are pressed on the first digital joystick you see X,Z and the arrows displayed, the same as if you had pressed these buttons on a 464/6128 Plus or CPC. Pressing Pause displays "P".

Accessing the Plus hardware improvements

The Plus and GX4000 cartridges access the Plus hardware improvements, but specific software can be created using the extra features without the need of cartridge hardware (contrary as it was claimed by Amstrad in 1991). The extra features are not locked by a hardware mechanism but only by a special 17 bytes-length sequence send to the CRTC. So, it's possible for everyone to create his/her own software on the Plus, using the extra features available through a ASIC I/O page. Except the extra-features, the 464 and 6128 Plus machines are almost fully compatible with the classic CPC generation. Some minor differences are noticeable in the components (PPI, CRTC, Gate ArrayGate Array) contained in the ASIC and in the interrupt mechanism in vectorised mode.

Vapourwares

Bootlegs

Lately (as of May 2007) several instances ofbootleg cartridges have appeared. These are not original releases and, although they could run without any problems, caution should be exercised when buying. What is more, their collectible/historical value is doubtful. For more details, see Bootleg Cartridges and here

Amstrad CSD

The Amstrad CSD was a system containing a 464PLUS motherboad and an additionnal Mainboard enabling to switch beteween 12 different game (or whatever) Cartridges. The System was supplied with some sort of JukeBox OS Cartridge.

It was used as a demonstration system at retailers and shops were the Amstrad PLUS range was sold.